How to find out the exact Frequency of F-Curve Modifiers
It looks like the base modifier is set to f(t) = sin(t) . That is to say, f(0) = 0, f(pi/2) = 1, f(pi) = 0 and f(3*pi/2) = -1

So the frequency is 2 * pi (The curve repeats itself every 6,283185307... units).
If you want to tweak the frequency, say you want a cycle every 10 frames, multiply the phase by 2 * pi and divide by 10.